The present invention relates to a fuel injection timing control device for an internal combustion engine which comprises means for advancing the injection timing when the engine speed is very low such as during starting.
Fuel injection pumps for internal combustion engines, especially of the combustion ignition or Diesel type, preferably comprise means for regulating the amount of fuel injection and also the timing in the engine cycle at which the fuel is injected. It is known to control the latter function, especially in distribution type injection pumps, by means of a hydraulic injection timing control device which advances the injection timing in generally proportional relation to the pressure of an engine driven low pressure fuel supply pump. The supply pump is driven by the engine in such a manner that the supply pump pressure increases as the engine speed increases.
However, it is desirable to advance the injection timing under extremely low engine speed operating conditions, such as during starting, in order to reduce the emission of unburned fuel constituents from the engine which appear as black smoke. Heretofor, the injection timing control devices which have been provided for engines are operative to advance the injection timing only as the engine speed increases, with substantially zero advance at low engine speed, thereby leaving unsolved the above mentioned problem of pollutant emission.